ZFS: optimize, install pkgs only when required

roles/zfs/defaults/main.yml

@@ -0,0 +1,6 @@
+---
+ZFS_PKGS:
+  - kernel-devel
+  - "@Development tools"
+  - dkms
+  - zfs

roles/zfs/tasks/main.yml

@@ -43,13 +43,8 @@
 
 - name: install zfs and dkms
   package:
-    name: "{{ item }}"
+    name: "{{ ZFS_PKGS | difference(ansible_facts.packages) }}"
     state: present
-  with_items:
-  - kernel-devel
-  - "@Development tools"
-  - dkms
-  - zfs
   register: zfs_installed
   when: ansible_distribution in ["CentOS" , "Red Hat Enterprise Linux", "Fedora" ] and not is_atomic